The present disclosure relates generally to air conditioning units for use in a hazardous environment where flammable gases or vapors may exist. In particular, the present disclosure relates to air conditioning units which prevent gases from being ignited by encapsulating sparking components, using solid-state switching devices, and/or wiring circuits in such a way that open contacts do not contain enough energy to produce a spark capable of igniting the atmosphere.
In many applications, it is necessary to provide air conditioning or refrigeration systems in locations where flammable gases or vapors exist. For example, a worker may be surrounded by atmospheric conditions conducive to danger. An oxygen rich atmosphere might be particularly conducive to flash fire caused by a stray spark. A similar condition could exist in a dust laden atmosphere or in an atmosphere which includes flammable vapors. At such locations, it is necessary to provide protection against the ignition of such flammable gases or vapors, in order to prevent the occurrence of highly undesired explosions.
In the prior art, explosion-proofing techniques included creating a purged and pressurized system to create a non-hazardous environment, or adding a large cast explosion proof enclosure to contain any undesired explosions and placing any sparking devices within the explosion proof enclosure. However, these explosion proof techniques were unduly complicated and expensive because purge and pressurization devices required shop air, and large cast explosion proof enclosures are bulky and expensive. Further, these bulky enclosures significantly increased the size of the hazardous location rated air conditioners.